1. Field of the Invention
The present invention relates to a guidance route search method of searching for an optimal guidance route from a starting point to a destination in a navigation device and, more particularly, to a guidance route search method of searching for a guidance route matching a user's needs.
2. Description of the Related Art
A known vehicle navigation device includes a map-data storage section for storing map data such as a DVD (Digital Versatile Disk)—ROM or the like, a display for displaying a map image, and a vehicle position detector for detecting a present position and a present traveling direction of a vehicle, such as a gyro, a GPS (Global Positioning System) receiver, a vehicle speed sensor, and the like. The navigation device reads from the map-data storage section the map data containing information on the present position of the vehicle, and draws the map image covering the present vehicle position and its surroundings based on the map data, while also drawing a vehicle position (location) mark superimposed on the map image. The navigation device makes the map image scrollable, or makes the vehicle position mark movable in accordance with the travel of the vehicle with the map image being stationary on a screen, thus allowing a user to understand the present traveling position of the vehicle at a glance.
Generally, the vehicle navigation device has the function of route guidance that enables the user to easily travel an appropriate route to the desired destination without taking a wrong path. This route guidance function automatically searches for a route connecting the starting point to the destination and having a lowest cost, by performing a simulated calculation, such as the lateral search method or the Dijkstra method, using the map data, and stores the resultant searched route as a guidance route. During traveling, the route guidance function draws the guidance route on the map image of the screen by a solid line in a different color from that of the other roads. When the vehicle is approaching within a certain distance of an intersection to change course on the guidance route, the route guidance function draws an arrow at the intersection on the map image to indicate the traveling direction beyond the intersection, thus guiding the user to the destination.
The aforesaid cost is set in terms of a value obtained from multiplying a travel distance of a road by a constant corresponding to the width of the road, the type of the road (general road, or highway), the direction of a turn, namely a right turn or left turn, or the like, or in terms of a time required for the vehicle to pass through the road on the basis of the distance traveled thereon. Thus, the cost is a numeric value indicating the degree of propriety as the guidance route. Even if there are two roads with the same travel distance, the cost depends on, for example, whether the user makes use of a highway or not, or whether the user gives a higher priority to the time or the distance.
However, the guidance route which is automatically searched for or found by the vehicle navigation device does not always meet the user's needs or preferences. For example, the following cases may occur: a case where the resultant guidance route includes a road with a heavy traffic jam anticipated, or a road without fine scenery; or a case where there is another road not included in the guidance route and which the user is accustomed to traveling. In such cases, the conventional navigation device is designed to set a transit point (pass-through point) and to search for a guidance route including the transit point, thereby handling the described problems to some extent. Even though the transit point is previously set as described above, a guidance route is not necessarily searched for or found that leads to the transit point through the user's desired road. As is often the case with the conventional navigation device, the resultant searched route does not match or satisfy the user's needs.
Another known navigation device has been proposed that searches for a plurality of guidance routes at one time to present them to a user, and requests the user to select his/her desired one from these guidance routes. However, the plurality of guidance routes searched for does not necessarily include the user's desired route.
Conventionally, still another known navigation device has been developed for previously designating a road (Avoidance Street) which a user would not like to pass through. In this device, although a searched guidance route bypasses the road designated by the user, the resultant searched guidance route does not always fit the user's needs.